Known charge generating materials having sensitivity in the near infrared region which can be used in electrophotographic photoreceptors include squarylium pigments, bisazo pigments, trisazo pigments, and phthalocyanine pigments. Of these materials, phthalocyanine pigments have recently been attracting particular attention because of their high sensitivity, and various species thereof having different crystal forms have hitherto been proposed for use as a charge generating material of electrophotographic photoreceptors. For example, JP-A-1-221459 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes that gallium phthalocyanine species showing intense X-ray diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) of 6.7.degree., 15.2.degree., 20.5.degree., and 27.0.degree.; at Bragg angles of 6.7.degree., 13.7.degree., 16.3.degree., 20.9.degree., and 26.3.degree.; or at Bragg angles of 7.5.degree., 9.5.degree., 11.0.degree., 13.5.degree., 19.1.degree., 20.3.degree., 21.8.degree., 25.8.degree., 27.1.degree., and 33.0.degree.; or having an intense peak at a Bragg angle of 27.1.degree. with the intensities of the other peaks being not more than 10% of that peak are effective as a charge generating material. Further, a novel dichlorotin phthalocyanine crystal and its combination with a charge transporting material are disclosed, e.g., in JP-A-1-144057 and JP-A-62-119547.
JP-A-62-67094 discloses oxytitanium phthalocyanine having the most intense diffraction peak at a Bragg angle (2.theta..+-.0.2.degree.) of 27.3.degree.. Although this particular oxytitanium phthalocyanine has very high sensitivity, it has poor stability on repeated use, poor crystal form stability in a coating composition, and insufficient dispersibility. In order to settle these problems, it has been proposed to incorporate a small amount of substituted phthalocyanine as described, e.g., in JP-A-3-9962, JP-B-55-27583, and JP-B-54-44684 (the term "JP-B" as used herein means an "examined Japanese patent publication"). In this case, however, since substituted phthalocyanine incorporated is markedly different from unsubstituted phthalocyanine in crystal form, mixing them gives rise to another problem, such as reduction in electrophotographic characteristics.
On the other hand, various mixed crystals comprising oxytitanium phthalocyanine and other phthalocyanine species are known as disclosed, e.g., in JP-A-1-142658, JP-A-2-70763, JP-A-2-170166 and JP-A-2-272067.
The inventors have studied various phthalocyanine crystal forms in pursuit of an electrophotographic photoreceptor with excellent electrophotographic characteristics and productivity and found, as a result, a novel crystal form of a halogenogallium phthalocyanine having high sensitivity as disclosed in Japanese Patent Application No. Hei-3-116630. They also found various novel crystal forms of a dihalogenotin phthalocyanine as disclosed in Japanese Patent Application Nos. Hei-3-126489 and Hei-3-274872. It turned out, however, that the halogenogallium phthalocyanine is slightly inferior to the dihalogenotin phthalocyanine in stability to environmental changes and that the dihalogenotin phthalocyanine is, though very excellent in stability to environmental changes, slightly inferior to the halogenogallium phthalocyanine in sensitivity.